The method for the ring-opening polymerization of a norbornene monomer, such as dicyclopentadiene (DCPD) or methyl tetracyclododecene (MTD), in a mold, and the addition of an elastomer as an impact modifier, is well known.
For example, in Japanese Kokai patent No. Sho 58[1983]-129013, a method for the manufacture of a thermosetting DCPD homopolymer using a metathesis catalyst by the reaction injection molding (RIM) method is disclosed.
If an elastomer is added to one or both of the two reaction solutions in this case, it has been shown that the flexural modulus is decreased somewhat but the impact strength is increased by 5-10 times.
Furthermore, in Japanese Kokai Patent No. Sho 59[1984]-51911, RIM of cyclic olefins containing norbornene rings, such as DCPD and MTD, has been disclosed. Even in this bulk polymerization method, the mixing of an elastomer as an impact modifier into the monomer reaction solution is shown.
The ring-opening polymers in these disclosed methods have relatively good performance in terms of a variety of physical properties required in engineering plastics, such as impact strength, high modulus of elasticity, heat resistance, etc. However, in regards to the stringent performance required to date, it is still difficult to say that they are necessarily sufficient.
For example, it has been pointed out that the glass transition temperature (Tg) of the DCPD homopolymers obtained by these methods is insufficient. As an improvement method, a method has been proposed in which comonomers, like tetracyclododecadiene, trimethylolpropane-tris(5-norbornene-2-carboxylate), etc., having two or more reactive double bonds, are copolymerized so that the number of crosslinkings is increased by cleavage during the polymerization, see Japanese Kokai Patent No. Sho 61[1986]-179214. However, in this method, special comonomers which are difficult to obtain are used.
Furthermore, U.S. Pat. No. 4,703,098, discloses the use of a mixture of DCPD and its oligomers, obtained by the heat treatment of DCPD. From said heat-treated product, it is possible to manufacture a thermosetting resin with an improved glass transition temperature. However, in the storage of said heat-treated product, a white micropowder is deposited which makes handling thereof difficult.
For example, if the concentrations of trimers or tetramers of cyclopentadiene present in the heat-treated product are high, part of the trimers and tetramers form a white micropowder which is precipitated. This phenomenon is especially strong when the concentrations of the trimers and tetramers are more than 15 weight percent or the storage temperature is less than 10.degree. C. Owing to this settling phenomenon, the piping of the reaction equipment becomes plugged and variations in the compositions or physical properties of the thermosetting resins occur. In order to prevent these problems, the heat-treated product is heated during storage, the storage tank is stirred, or other troublesome operations are required. In addition, with an increase in the trimers and tetramers, although the glass transition temperature will increase, the impact resistance will be reduced. In particular, there is a drawback in that the impact resistance is reduced after the heat treatment test.